When a hearing instrument is removed from the ear canal, the increased acoustic coupling between the receiver (loudspeaker) and the microphone can cause howling or feedback. Furthermore, the device is typically not in use when removed. Therefore, knowledge that the device has been removed can be used to lower the acoustical gain to prevent feedback and/or to reduce power consumption by switching the unit off or entering a low-power standby mode.
Conversely, when the unit is re-inserted, knowledge that the device has been inserted can be used to automatically restore gain and power. In a communications headset, this information can be used to automatically answer an incoming call or to terminate a completed call.
Additionally, a hearing instrument is designed to have an acceptable acoustic response when sealed with a user's ear. However, when initially fitted or when in later use, the hearing instrument may not form a proper seal. Accordingly, an audiologist or user may need to determine whether the hearing instrument has formed a proper seal.